1. Field of the Inventions
The inventions relate to a head mounted or helmet mounted passive and active infrared imaging system, and more particularly to an infrared imaging system for an advanced rescue vision system. One embodiment relates to a head/helmet mounted passive infrared imaging system; and another embodiment relates to an active head/helmet mounted infrared imaging system. Both systems share the same objective lens, uncooled focal plane array, image processing electronic circuit, display and head/helmet mount.
2. Background Information
Infrared means that the wavelength of infrared radiation is longer than visible light (from 0.38xcexc to 0.78xcexc). Infrared light shares many of the properties of visible light, but its different wavelength has several unique characteristics. For instance, materials that are opaque to visible light may be transparent to infrared, and vice-versa. Infrared cannot be seen by human eye, and infrared is much less subject to scattering and absorption by smoke or dust than visible thus the IR imager can see through smoke and dust.
Unlike visible light, which is given off by ordinary objects only at very high temperatures, infrared energy is emitted by all objects at ordinary temperatures higher than 0xc2x0 K. This means that infrared energy is all around us all the time, even in the dark Different objects give off varying amounts of infrared energy, depending on the temperatures of the objects and their emissivities. Passive IR cameras are designed to sense differing amounts of infrared energy coming from the various areas of a scene by focal plane array detector and to convert them to corresponding intensities of visible light by electronics for display purposes. This permits true see-in-the-dark capability and the ability to observe the thermal properties in all light conditions.
Contemporary passive infrared imagers use cryogenic coolers, complex IR optics and costly IR sensor materials, and their consequent high cost restrict their applications such as for fire fighting and security. In this invention, Uncooled Focal Plane Array (UFPA) will be adopted.
In a staring imager, a 2D FPA is placed at the focal plane of the lens. One IR sensor element is used for each pixel in the display, and no moving mirrors are used. The requirement on the response time of the IR sensor element is greatly reduced, to about the frame time of the imager (typically {fraction (1/30)} sec). The dwell time of the image on each pixel is increased by about 100 compared to a scanning imager, improving the relative sensitivity of the staring imagery by about 10, which is desirable for specialised military purposes. These advantages of staring operation also allow uncooled thermal sensors to produce good quality IR images.
Uncooled silicon microbolometer (MBT) and Barium Strontium Titanate (BST) arrays represent a new capability in staring imager development, allowing excellent IR imaging performance at much lower cost, size and weight. Uncooled imager sensitivity is now better than 0.04xc2x0 C., surpassing the sensitivity of some cooled scanned systems currently in military service and even competing with cooled staring systems in some applications.
Some of the most significant advantages of uncooled MBT and BST IR imagers in comparison with cooled IR imagers are: no cooling system, lower unit and life cycle cost, reduced power consumption, smaller size and lighter weight, higher system reliability, no audible cooler or scanner noise, and capability for multispectral response.
The extreme thermal environment experienced by equipment utilized in front line fire fighting applications (transition from 20xc2x0 C. ambient to 1,000xc2x0 C. in seconds), together with weight and size constraints tend to limit the level of thermal insulation which can be used to protect the sensor. However, by utilizing uncooled IR detector technology together with advanced optics and thermal management technique, compact IR imager can be manufactured which withstands these environments.
By matching the field of view of the Helmet Mounted IR sensor to that of the display, the fire fighter is able to see the IR image with the 1:1 surroundings and the 1:1 xe2x80x9creal worldxe2x80x9d. This combination offers hands-free operation together with unrivalled manoeuvrability.
However, current helmet mounted passive IR imagers using UFPAs have many shortcomings such as: large, heavy, expensive, the Germanium (Ge) lens will turn to opaque within 20 minutes in fire fighting, there is a parallax between the camera and viewer, the user can not speak under mask, the display blocks user""s normal vision, and the IR system can not fit the mask. The purpose of this invention is to overcome all these problems.
It is well known that the passive IR image only represents the temperature and emissivity differences of the targets not their detailed shape differences, therefore it is hard to distinguish a person if he is Mr. Smith or Mr. Johnson. In this invention, an near infrared eye-safe laser diode is integrated to the passive system to illuminate the target and get its reflective image from the same UFPA of BST, thus very sharp image can be obtained. To identify friend or foe in battle field and security applications becomes possible.
In fire fighting, the temperature is very high. The passive IR imager can not detect a person behind the firewall. Eventually, it will be saturated by the strong high-temperature environmental IR radiation and thus becomes useless. It is an unsolved problem in the history. The purpose of the active IR imaging system of this invention is to solve this problem.
Passive System
The innovative head/helmet mounted passive infrared imaging system design is shown in FIG. 1, and its functional block diagram is shown in FIG. 2. The detailed explanation of the diagram will be given in the next paragraph of preferred embodiments. The invention includes following new ideas/technologies:
Use uncooled focal plane array to eliminate the cooling system;
Design non-Ge objective lens and window and use new manufacturing methods to cover the whole spectrum from near infrared to long infrared, increase the sustained temperature, and reduce the cost to half of the old optics;
Adopt separated imaging head and body configuration to realise compact head design;
Design special Liquid Crystal Display (LCD) to enhance the image contrast without blocking user""s normal vision;
Eliminate the parallax between the camera and display to see the correct target location;
Design special mechanical mounting to clip the system on the head mount or helmet and release the system from the head mount or helmet easily without using any tool;
Use fly logic or neural network pattern recognition chip to distinguish human victim or fire from background;
Design special adjustment mechanism to let the LCD has forward/back, up/down, and tilt adjustments to fit any mask;
Adopt piezoelectric film contacting to user""s forehead or neck as microphone to speak under mask without using mouth;
Use voice control chip to perform hands-free operation;
Design wireless audio and video transceiver to link the frontier with the rear headquarters.
Reduce the weight and cost to half of the contemporary systems.
Active System
The innovative active IR imaging system is shown in FIG. 17 of the preferred embodiment. The system has following new ideas/technologies:
Integrate a very small eye-safe laser diode at wavelength around 1.5xcexc on the head mount or helmet to illuminate the targets;
Use the same non-Ge objective lens to get the active IR image because the lens has high transmittance from near infrared to long infrared;
Use same UFPA of BST to image the targets because the response of the BST is 1-35xcexc;
See through the smoke, dust, and darkness;
Get clear image and distinguish the friend and foe;
See through the firewall and detect a person behind the firewall;
Reduce the weight and cost to ⅕ of the passive system if the active system is a stand along system.